Finger biometric sensor including drive signal level updating and related methods

ABSTRACT

A finger biometric sensor may include an array of finger biometric sensing pixels and processing circuitry coupled thereto. The processing circuitry may be capable of acquiring initial data from the array based upon an initial drive signal level and with a finger positioned adjacent the array, and determining an updated drive signal level based upon the initial data. The processing circuitry may also be capable of acquiring finger biometric data from the array of finger biometric sensing pixels based upon the updated drive signal level and with the finger positioned adjacent the array.

FIELD OF THE INVENTION

The present invention relates to the field of electronics, and, moreparticularly, to electronic devices including finger biometric sensorsand related methods.

BACKGROUND

Fingerprint sensing and matching is a reliable and widely used techniquefor personal identification or verification. In particular, a commonapproach to fingerprint identification involves scanning a samplefingerprint or an image thereof and storing the image and/or uniquecharacteristics of the fingerprint image. The characteristics of asample fingerprint may be compared to information for referencefingerprints already in a database to determine proper identification ofa person, such as for verification purposes.

A particularly advantageous approach to fingerprint sensing is disclosedin U.S. Pat. No. 5,963,679 to Setlak and assigned to the assignee of thepresent invention. The fingerprint sensor is an integrated circuitsensor that drives the user's finger with an electric field signal andsenses the electric field with an array of electric field sensing pixelson the integrated circuit substrate. Such sensors are used to controlaccess for many different types of electronic devices such as computers,cell phones, personal digital assistants (PDA's), and the like. Inparticular, fingerprint. sensors are used because they may have a smallfootprint, are relatively easy for a user to use and they providereasonable authentication capabilities.

In some recent applications, the sensor may desirably capture images offingerprint patterns from fingers that are farther away from the sensorarray than is typical with today's technologies. Unfortunately as thefinger gets farther away from the sensor array (for example when arelatively thick dielectric lies between the sensor array and thefinger), the spatial field strength variations that represent thefingerprint pattern become weaker. One way to compensate for this lossof spatial pattern strength is to increase the voltage of the signalsthat generate the field between the finger and the sensor array, alsoknown as the drive signal. The fingerprint spatial pattern strengthincreases proportionately.

However, the detected signals generated from the sensor array and basedupon placement of the use finger adjacent the sensor array arerelatively small compared to the drive signal. Thus, these relativelysmall detected signals may be increasingly difficult to process alongwith the relative high drive signal, limiting measurement resolution ofthe detected signals, for example. Amplifier and processing stages thatread and process the detected signals may add additional noise. Anothersource of noise may be fixed pattern noise from the sensor array, whichalso may make it increasingly difficult to measure the detected signals.

SUMMARY

A finger biometric sensor may include an array of finger biometricsensing pixels and processing circuitry coupled to the array. Theprocessing circuitry may be capable of acquiring initial data from thearray based upon an initial drive signal level and with a fingerpositioned adjacent the array, and determining an updated drive signallevel based upon the initial data. The processing circuitry may also becapable of acquiring finger biometric data from the array based upon theupdated drive signal level and with the finger positioned adjacent thearray.

The finger biometric sensor may further include a finger couplingelectrode adjacent the array of finger biometric sensing pixels. Theprocessing circuitry may further include drive circuitry coupled to thefinger coupling electrode. The drive circuitry may be capable ofgenerating a range of drive signal levels. The initial drive signallevel may be at a maximum of the range of drive signal levels, forexample.

The processing circuitry may be capable of determining whether thefinger is stable. The processing circuitry may be capable of determiningthe updated drive signal level when the finger is stable, for example.

The processing circuitry may include a digital-to-analog converter (DAC)and at least one gain stage coupled thereto. The processing circuitrymay be capable of acquiring the initial data from a plurality ofspaced-apart sub-arrays of the array of finger biometric sensing pixels.The plurality of spaced apart sub-arrays may be are arranged in acheckerboard pattern, for example. The array of finger biometric sensingpixels may include an array of electric field finger sensing pixels.

An electronic device aspect may include a housing and wirelesscommunications circuitry carried by the housing. The finger biometricsensor may be carried by the housing.

A method aspect is directed to a method of acquiring finger biometricdata. The method includes acquiring initial data from an array basedupon an initial drive signal level and with a finger positioned adjacentthe array of finger biometric sensing pixels. The method also includesdetermining an updated drive signal level based upon the initial data,and acquiring the finger biometric data from the array based upon theupdated drive signal level and with the finger positioned adjacent thearray.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an electronic device according to anembodiment.

FIG. 2 is a schematic block diagram of the electronic device of FIG. 1.

FIG. 3 is a flowchart of acquisition of finger biometric data from thefinger sensor of FIG. 2.

FIG. 4 is a schematic block diagram of a portion of finger biometricsensor according to another embodiment.

FIG. 5 is a more detailed schematic diagram of the portion of the fingerbiometric sensor of FIG. 4.

FIG. 6 is a flowchart of acquisition of finger biometric data from thefinger sensors of FIG. 4.

DETAILED DESCRIPTION

The present embodiments will now be described more fully hereinafterwith reference to the accompanying drawings, in which preferredembodiments of the invention are shown. These embodiments may, however,take many different forms and should not be construed as limited tothose set forth herein. Rather, these embodiments are provided so thatthis disclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Like numbers referto like elements throughout, and prime notation is used to indicatesimilar elements in alternative embodiments.

Referring initially to FIGS. 1-2, an electronic device 20 is nowdescribed. The electronic device 20 illustratively includes a portablehousing 21 and a device processor 22 carried by the portable housing.The electronic device 20 is illustratively a mobile wirelesscommunications device, for example, a cellular telephone. The electronicdevice 20 may be another type of electronic device, for example, atablet computer, laptop computer, etc.

Wireless communications circuitry 25 (e.g. a wireless transceiver,cellular, WLAN Bluetooth, etc.) is also carried within the housing 21and coupled to the device processor 22. The wireless transceiver 25cooperates with the device processor 22 to perform at least one wirelesscommunications function, for example, voice and/or data communication.In some embodiments, the electronic device 20 may not include a wirelesstransceiver 25.

A display 23 is also carried by the portable housing 21 and is coupledto the device processor 22. The display 23 may be a liquid crystaldisplay (LCD), for example, or may be another type of display, as willbe appreciated by those skilled in the art. A device memory 26 is alsocoupled to the processor 22.

A finger-operated user input device, illustratively in the form of apushbutton switch 24, is also carried by the portable housing 21 and iscoupled to the device processor 22. The pushbutton switch 24 cooperateswith the device processor 22 to perform a device function in response tomanipulation of the pushbutton switch. For example, a device functionmay include a powering on or off of the electronic device 20, initiatingcommunication via the wireless communications circuitry 25, and/orperforming a menu function.

More particularly, with respect to a menu function, the device processor22 may change the display 23 to show a menu of available applicationsbased upon pressing of the pushbutton switch 24. In other words, thepushbutton switch 24 may be a home switch or button, or key. Of course,other device functions may be performed based upon the pushbutton switch24. In some embodiments, the finger-operated user input device 24 may bea different type of finger-operated user input device, for example,forming part of a touch screen display. Other or additionalfinger-operated user input devices may be carried by the portablehousing 21.

The electronic device 20 includes a finger biometric sensor 50, whichmay be in the form of one or more integrated circuits (ICs). The fingerbiometric sensor 50 includes an array of finger biometric sensing pixels31 that may be part of an IC carried by the pushbutton switch 24 tosense a user's finger 40 or an object placed adjacent the array ofelectric field sensing pixels. Each pixel of the array of fingerbiometric sensing pixels 31 may be an electric field sensing pixel ofthe type as disclosed in U.S. Pat. No. 5,940,526 to Setlak et al., forexample, assigned to the present assignee, and the entire contents ofwhich are incorporated herein by reference.

The finger biometric sensor 50 includes processing circuitry 51 whichmay be in the form of one or more processors and a memory coupledthereto. Other circuitry may be included in the processing circuitry 51,as will be described in further detail below.

Referring, now to the flowchart 100 in FIG. 3, beginning at Block 102,acquisition of finger biometric data from the finger biometric sensor 50is now described. The processing circuitry 51, at Block 104 acquiresinitial data from the array of finger biometric sensing pixels 31 basedupon an initial drive signal level and with a finger 40 positionedadjacent the array of finger biometric sensing pixels.

The processing circuitry 51 determines an updated drive signal levelbased upon the initial data (Block 106). The processing circuitry 51, atBlock 108, acquires finger biometric data from the array of fingerbiometric sensing pixels 31 based upon the updated drive signal leveland with the finger 40 positioned adjacent the array of finger biometricsensing pixels before ending at Block 110.

In some embodiments, the processing circuitry 51, for example, may alsocooperate with the array of finger biometric sensing pixels 31 todetermine a finger match based upon the image data. More particularly,the processing circuitry 51 may determine a finger match based uponenrollment image data stored in memory and a sufficient amount ofgenerated image data. Enrollment data may typically be collected over aseries of regions of a finger that are then assembled or composited intoa larger region. The match or generated image data may be smaller, butstill having an area or number of matching features to provide a desiredrate of matching.

In some embodiments, the processing circuitry 51 may also determine alive finger based upon spoof data. More particularly, the processor 51may determine a live finger based upon a complex impedance and/or bulkimpedance measurement.

In some embodiments, the processing circuitry 51 may cooperate with thearray finger biometric sensing pixels 31 to perform a navigationfunction, for example. Of course the processing circuitry 51 maycooperate with the array finger biometric sensing pixels 31 and/or othercircuitry to perform other or additional functions, as will beappreciated by those skilled in the art.

It should be understood that in some embodiments, the processingcircuitry 51 may be part of or included in the device processor 22. Inother words, the functionality described herein with respect to theprocessing circuitry 51 may be performed by the device processor 22,another processor, or shared between or among processors.

Referring now to FIGS. 4 and 5, further details of a finger biometricsensor 50′ are described. The finger biometric sensor 50′ also includesswitching circuitry 32′ coupled to the array of finger biometric sensingpixels 31′ and gain stages 60 a′-60 d′. The switching circuitry 32′ iscapable of acquiring finger biometric data from each of a plurality ofsub-arrays 33 a′-33 e′ of the array of finger biometric sensing pixels31′. More particularly, the switching circuitry 32′ is capable ofsequentially generating output data for adjacent regions of the array offinger biometric sensing pixels 31′ or sub-arrays 33 a′-33 e′, or moreparticularly, for each finger biometric sensing pixel 35′. In an 88×88array of finger biometric sensing pixels, there are 7744 fingerbiometric sensing pixels and 7744 corresponding switches. Of course,additional switches may be used, as will be appreciated by those skilledin the art.

The finger biometric sensing device 50′, and more particularly, theprocessing circuitry 51′ includes drive circuitry 44′ capable ofgenerating a drive signal coupled to the array of finger biometricsensing pixels 31′. The array of finger biometric sensing pixels 31′cooperates with the drive circuitry 44′ to generate a drive signal ordetected signal based upon placement of a finger 40′ adjacent the arrayof finger biometric sensing pixels. The gain stages 60 a′-60 d′ arecoupled together in series and define summing nodes 61 a′-61 b′ betweeneach pair of adjacent gain stages.

The first gain stage 60 a′ may be in the form of one or more variablegain amplifiers 63 a′ defining front end amplifiers, each respectivelycoupled to a finger biometric sensing pixel from the array of fingerbiometric sensing pixels 31′. The first gain stage 60 a′ is input withthe detected signal at a raw signal level. An output of the first gainstage 60 a′ is coupled to the first summing node 61 a′. For an 8-channelimplementation (e.g., for an 88×88 array of finger biometric sensingpixels divided into eleven 8×8 regions), there are 8 instances of theillustrated first gain stage 60 a′.

The second gain stage 60 b′ may also be in the form of one or morevariable gain amplifiers 63 b′ defining AC amplifiers. Each amplifier 63b′ of the second gain stage 60 b′ has an input coupled to the firstsumming node 61 a′. A capacitor 64′ or other impedance device may becoupled between the first summing node 61 a′ and the first gain stage 60a′. The second gain stage 60 b′ also processes the input signal at a rawsignal level. For an 8-channel implementation (e.g., for an 88×88 arrayof finger biometric sensing, pixels divided into eleven 8×88 regions),there are 8 instances of the illustrated second gain stage 60 b′.

The third gain stage 60 c′ may be in the form of one or more pairs ofvariable gain amplifiers 63 c′, 63 d′ defining a correlated doublesampler (CDS). More particularly, the third gain stage 60 c′ may includeodd and even variable gain amplifiers 63 c′, 63 d′ for each channel. Foran 8-channel implementation, there are 8 instances of the illustratedthird gain stage 60 c′. The output of each of the odd and even variablegain amplifiers 63 c′, 63 d′ of the third gain stage 60 c′ are input toa multiplexer 66′. As will be appreciated by those skilled in the art,the multiplexer 66′ may be a 16:1 multiplexer for an 8 channelimplementation. The output of the multiplexer 66 is summed, at thesecond summing node 61 b′, with an output from a seconddigital-to-analog converter (DAC) 72′, which will be described infurther detail below. The third gain stage 60 c′ also processes theinput signal at a raw signal level.

The fourth gain stage 60 d′ may also be in the form of one or morevariable gain amplifiers 63 e′. The variable gain amplifier 63 e′ mayhave an input coupled to the second summing node 61 b′ and an outputcoupled to the third summing node 61 c′. The fourth gain stage 60 d′processes the input signal at a feature signal level. Of course, whilefour gain stages 60 a′ 60 d′ are illustrated and described, there may beadditional gain stages.

The finger biometric sensor 50′ includes a finger coupling electrode 47′adjacent the array of finger biometric sensing pixels 31′. The drivecircuitry 44′ may be in form of a drive signal generator, or voltagegenerator, coupled to the finger coupling electrode 47′.

The array of finger biometric sensing pixels 31′ and the gain stages 60a′-60 d′ have a circuit reference associated therewith. The circuitreference is to be coupled to a device ground so that the drivecircuitry 44′ drives the finger coupling electrode 47′ with respect tothe circuit reference and the device ground.

The finger biometric sensor 50′ also includes drive signal nullingcircuitry 45′ coupled to the gain stages 60 a′-60 d′. As will beappreciated by those skilled in the art, relatively high voltage drivesignals may result in relatively large common mode voltages appearing onthe detected signal generated from the array of finger biometric sensingpixels 31′. Since the drive signal generally carries no usefulinformation, it may be particularly desirable to reduce or eliminate itas early as possible in the signal chain. Specifically, small spatialvariations in electric field intensity in the presence of a relativelylarge average field intensity may be measured.

The drive signal nulling circuitry 45′ is capable of reducing therelatively large drive signal component from the detected signal. Thedrive signal nulling circuitry 45′ includes digital-to-analog converter(DAC) 46′ capable of generating an inverted scaled replica of the drivesignal for the gain stages 60 a′-60 d′. More particularly, the DAC 46′is coupled to the first summing node 61 a′. A memory may be coupled tothe DAC 46′.

An output analog-to-digital converter (ADC) 56′ may be coupleddownstream from the gain stages 60 a′-60 d′. More particularly, theoutput ADC 56′ may be coupled to the fourth gain stage 60 d′ and mayhave a dynamic range. In some embodiments, a memory may be coupled tothe ADC 56′. Control circuitry is capable of adjusting the fourth gainstage 60 d′, and in some embodiments, other and/or additional gainstages so that an output thereof is within the dynamic range of outputADC 57′.

Referring now additionally to the flowchart 130′ in FIG. 6, beginning atBlock 132′, further details of the finger biometric 50′ sensor andacquisition of finger biometric data from the finger biometric sensorare now described. At Block 134′, the processing circuitry 51′ acquiresinitial data from a subset of the array of finger biometric sensingpixels 31′ based upon an initial drive signal level. More particularly,the drive circuitry 44′, which generates a range of drive signal levels,generates the initial drive signal level to be at a maximum of the rangeof drive signal levels. The initial data may include finger stabilitybiometric data, impedance data, and ridge/flow data, for example. Ofcourse, other and/or additional types of data may form the initial data,and the initial data may not be limited to finger data.

At Block 136′, the processing circuitry 51′ determines whether a fingeris stable relative to the array of finger biometric sensing pixels 31′based upon the initial data, and more particularly, finger stabilitybiometric data. Determining whether a finger is stable may includechecking for stability and motion. The processing circuitry 51′ acquiresfinger stability biometric data from a subset of the array of fingerbiometric sensing pixels 31′. As illustrated in FIG. 4, the subset ofthe array of finger biometric sensing pixels 30′ includes spaced apartsub-arrays 33 a′-33 e′ from five regions of finger biometric sensingpixels and arranged in a checkerboard pattern. Each sub-array 33 a′-33e′ may include an 8×8 arrangement of pixels. In some embodiments, thesubset may include sub-arrays configured or arranged in other patternsand from other regions. Moreover, while five sub-arrays from fiveregions of finger biometric finger sensing pixels are illustrated, thesubset may include any number of sub-arrays and regions.

In the illustrated embodiment, the processing circuitry 51′ acquiresfinger stability data from each of the sub-arrays to determine whetherthere is a finger in the region. A region may be considered to includesub-arrays from a given column of the array of finger biometric sensingpixels 31′. Of course, in other embodiments, a region may be defined by,for example, a row of sub-arrays.

In some embodiments, prior to determining whether the finger is stable,the processing circuitry 51′ may determine whether a threshold number ofsub-arrays is sensing the finger. More particularly, the processingcircuitry 51′ may determine whether sub-arrays from at least threeregions (of the five) have acquired finger stability data indicative ofa finger. A setting of the DAC 46′ may be indicative of whether a fingeris in a given region. If less than three regions have acquired fingerstability data indicative of a finger, then the processing circuitry 51′again acquires data, for example, finger stability biometric data fromthe subset of the array of finger biometric sensing pixels 31′. Thethreshold number of sub-arrays may be any number, and, for example, maybe based upon the total number of sub-arrays.

Once the processing circuitry 51′ has determined that a threshold numberof sub-arrays is sensing a finger, the processing circuitry determineswhether a finger is stable relative to the array of finger biometricsensing pixels 31′ based upon the finger stability biometric data (Block136′). More particularly, the processing circuitry 51′ determineswhether the finger is stable based upon whether the threshold number ofsub-arrays indicates stability over successive data acquisitions. Adetermination of stability may be made when a difference between a lastsetting and current setting of the DAC 46′ are either less than a firstthreshold or greater than a second threshold that is greater than thefirst threshold. A determination of stability may also be made basedupon a difference between the difference between the last setting andthe current setting of the DAC 46′, and the last setting being less thana threshold, for example, 0 (i.e,(current−last)−(last−previousTolast)<threshold, or(N−(N−1))−((N−1)−(N−2), etc., where N is a current setting, N−1 is thelast setting, N−2 is the setting previous to the last setting and soon).

The processing circuitry 51′ may detect motion by generating a sum ofthe absolute value of pixel differences, as will be appreciated by thoseskilled in the art. The pixel values used. may be 8-bit pixel valuesafter a digital zoom. Other pixel values types may be used. The sum ofthe pixel difference is compared to yet another threshold, for example,a 16-bit programmable threshold. The sum of the pixel differences is tobe less than or equal to the programmable threshold for the finger to beconsidered not moving, stationary, or stable.

If the finger is not stable, the processing circuitry 51′ will againacquire initial data, for example, finger stability biometric data froma subset of the array (Block 134′), and thereafter determine whether thefinger is stable (Block 136′).

If the finger is stable (Block 136′) or not moving relative to the array31′, the processing circuitry 51′ determines an updated drive signallevel based upon the initial data. In particular, an average setting forthe DAC 46′ is calculated, and a target DAC setting is determined (Block138′). The average setting of the DAC 46′ may be based upon successiveacquisitions of data. The average DAC setting is compared to the targetDAC setting (Block 140′). The difference between the average and targetsettings of the DAC 46′ is used by the processing circuitry 51′ todetermine the updated drive signal level, and more particularly, todetermine what drive signal or excitation level is desired to arrive atthe target setting for the DAC (Block 142′). The processing circuitry51′ adjusts the drive signal level to the determined level (Block 144′).

The regions, for example, as described above, are sampled and theaverage setting of the DAC 46′ checked to see whether it is within atolerance or threshold range of the target setting of the DAC (Block146′). If, for example, the average setting of the DAC 46′ is outsidethe threshold range of the target setting of the DAC, the drive signallevel may again be updated (Block 138′). If the average setting of theDAC 46′ is within the threshold range, the processing circuitry 51′acquires finger biometric data from the array of finger biometricsensing pixels 31′ (Block 148′) before ending at Block 150′.

As will be appreciated by those skilled in the art, the measurementsignal path in the finger biometric sensor 50, a capacitive divider thatmay include a coating or dielectric layer over the sensor and pixelinput capacitance, may cause fixed pattern noise based upon smalldifferences in the coating or pixel input capacitance, for example. Ofcourse, other or additional components of the finger biometric sensor 50may cause fixed pattern noise. The apparent level of the fixed patternnoise generally varies with the level of the received signal. Since thesignal level is also a function of finger type, the fixed pattern noiselevel can vary from finger to finger making it increasingly difficultfor compensation.

By providing control of the drive signal level, the received carrierlevel may be changed to be within a relatively narrow range. Thus, fixedpattern noise, for example, may be maintained relatively constant andother or additional compensation therefore may be easier.

While a drive signal has been described herein, for example, withrespect to driving a voltage into the user's finger 40, it will beappreciated that the drive signal may not limited to just driving theuser's finger with the drive signal. In other words, the drive signalmay be positive or negative relative to the user's finger 40, or aground or circuit reference. For example, a drive signal may be managedby floating the ground of the amplifier in the first gain stage 60 a′,i.e., sense amplifier 63 a′, and connecting it to the drive signal. Insome embodiments, the finger coupling electrode 47′ may be coupled to adevice ground so that the drive circuitry 44′ drives the circuitreference with respect to the finger coupling electrode and the deviceground. This arrangement may be known as the inverted drive system orfloating ground system as will be appreciated by those skilled in theart. In other words, the drive signal level may be considered as anabsolute value or magnitude, while in some embodiments, the sign of thedrive signal may be positive or negative in the direction from thefinger coupling electrode 47′ to the array 31′.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. A finger biometric sensor comprising: anarray of finger biometric sensing pixels; and processing circuitrycoupled to the array of finger biometric sensing pixels and configuredto acquire initial data from the array of finger biometric sensingpixels at an initial drive signal level and with a finger positionedadjacent the array of finger biometric sensing pixels, determine anupdated drive signal level from the initial data, and acquire fingerbiometric data from the array of finger biometric sensing pixels at theupdated drive signal level and with the finger positioned adjacent thearray of finger biometric sensing pixels.
 2. The finger biometric sensorof claim 1, further comprising a finger coupling electrode adjacent thearray of finger biometric sensing pixels; and wherein the processingcircuitry further comprises drive circuitry coupled to the fingercoupling electrode.
 3. The finger biometric sensor of claim 2, whereinthe drive circuitry is configured to generate a range of drive signallevels; and wherein the initial drive signal level is at a maximum ofthe range of drive signal levels.
 4. The finger biometric sensor ofclaim 1, wherein the processing circuitry is configured to determinewhether the finger is stable.
 5. The finger biometric sensor of claim 4,wherein the processing circuitry is configured to determine the updateddrive signal level when the finger is stable.
 6. The finger biometricsensor of claim 1, wherein the processing circuitry comprises adigital-to-analog converter (DAC) and at least one gain stage coupledthereto.
 7. The finger biometric sensor of claim 1, wherein theprocessing circuitry is configured to acquire the initial data from aplurality of spaced-apart sub-arrays of the array of finger biometricsensing pixels.
 8. The finger biometric sensor of claim 7, wherein theplurality of spaced apart sub-arrays are arranged in a checkerboardpattern.
 9. The finger biometric sensor of claim 1, wherein the array offinger biometric sensing pixels comprises an array of electric fieldfinger sensing pixels.
 10. An electronic device comprising: a housing;wireless communications circuitry carried by the housing; and a fingerbiometric sensor carried by the housing and comprising an array offinger biometric sensing pixels, and processing circuitry coupled to thearray of finger biometric sensing pixels and configured to acquireinitial data from the array of finger biometric sensing pixels at aninitial drive signal level and with a finger positioned adjacent thearray of finger biometric sensing pixels, determine an updated drivesignal level from the initial data, and acquire finger biometric datafrom the array of finger biometric sensing pixels at the updated drivesignal level and with the finger positioned adjacent the array of fingerbiometric sensing pixels.
 11. The electronic device of claim 10, whereinthe finger biometric sensor further comprises a finger couplingelectrode adjacent the array of finger biometric sensing pixels; andwherein the processing circuitry further comprises drive circuitrycoupled to the finger coupling electrode.
 12. The electronic device ofclaim 11, wherein the drive circuitry is configured to generate a rangeof drive signal levels; and wherein the initial drive signal level is ata maximum of the range of drive signal levels.
 13. The electronic deviceof claim 10, wherein the processing circuitry is configured to determinewhether the finger is stable.
 14. The electronic device of claim 13,wherein the processing circuitry is configured to determine the updateddrive signal level when the finger is stable.
 15. The electronic deviceof claim 10, wherein the processing circuitry comprises adigital-to-analog converter (DAC) and at least one gain stage coupledthereto.
 16. The electronic device of claim 10, wherein the processingcircuitry is configured to acquire the initial data from a plurality ofspaced-apart sub-arrays of the array of finger biometric sensing pixels.17. The electronic device of claim 10, wherein the array of fingerbiometric sensing pixels comprises an array of electric field fingersensing pixels.
 18. The electronic device of claim 10, furthercomprising an input device carried by the housing; and wherein thefinger biometric sensor is carried by the input device.
 19. A method ofacquiring finger biometric data comprising: acquiring initial data froman array of finger biometric sensing pixels at an initial drive signallevel and with a finger positioned adjacent the array of fingerbiometric sensing pixels; determining an updated drive signal level fromthe initial data; and acquiring the finger biometric data from the arrayof finger biometric sensing pixels at the updated drive signal level andwith the finger positioned adjacent the array of finger biometricsensing pixels.
 20. The method of claim 19, wherein the initial drivesignal level is at a maximum of a range of drive signal levels.